Currently, a conventional printed circuit board fabrication technique is commonly used to fabricate an antenna feeder PCB (Printed Circuit Board, printed circuit board), and in particular, a conventional polytetrafluorethylene (PTFE) printed circuit board is used.
Conductor roughness of a transmission path in an antenna feeder circuit is one of major factors affecting passive inter-modulation (PIM) of an antenna. Therefore, transmission lines at internal and external layers both use copper foil of low roughness to improve PIM. A transmission line at an internal layer of a conventional multi-layer PTFE board is connected to a surface layer through a plated hole, and a current is transmitted in a direction along an interior wall of the plated hole. However, roughness of the wall of the plated hole affects PIM performance of the antenna feeder circuit.
On the one hand, a plated hole fabrication technique inevitably brings about a problem such as a rough hole and copper infiltration, which greatly affects PIM performance. On the other hand, a surplus wall of the plated hole also affects signal matching. To solve the foregoing problems, the prior art provides a method for connecting a line at an internal layer and a line at an external layer by means of welding. However, in this method, solder is used and occupies a large amount of space. In addition, this method is not suitable for mass production because of low welding efficiency.